The inventive concept relates to hard disk drives (HDD). More particularly, the inventive concept relates to a servo track writing system of a hard disk drive (HDD) and to the encoder of such a system.
An encoder is a device employed in various apparatus for measuring the movement or relative location of an object of the apparatus. To this end, a conventional encoder includes a light source, a first fixed grating, and a second grating connected to the object. Light emitted by the light source is transmitted through the first grating, and then is transmitted through or reflected by the second grating which is moving along with the object to which it is connected. The movement or relative location of the object is detected based on changes in the light transmitted by the two gratings. However, the accuracy of the encoder is often compromised due to backlash in the apparatus.
One apparatus that employs a conventional encoder of this type is a servo track writing system of an HDD. In a servo track writing system of an HDD, servo track information, by which a reading/writing head of the HDD can be moved rapidly and precisely to a desired position on the disk, is recorded in advance on servo tracks of the disk. This operation of recording the servo track information is referred to as servo track writing (STW). The encoder is used to track the location of the arm of the actuator which carries the reading/writing head in the STW operation. For example, the encoder may be connected to a pushpin which moves the actuator arm via a mechanical tool, and the amount of movement of the pushpin is detected to detect the movement of the actuator arm. However, backlash between the pushpin and the actuator, or vibrations and shocks generating during the STW operation may result in non-uniformity in the intervals between the servo tracks. Non-uniform intervals between the servo tracks prevents the disk from being able to have a high recording density, i.e., prevents the disk from being able to have a large number of tracks per inch (TPI).